The present invention relates to a thermoformable composite film, a process for producing a thermoformable composite film, the use of a solvent-free adhesive for applying a thermoplastic film to a film comprising cycloolefin copolymer in order to produce a thermoformable composite film, an extrusion coated film and a process for producing an extrusion coated film and use of the film as a packaging material.
To produce high-performance packaging, flexible films are molded to the shape of a tray or capsule using the action of heat and pressure and a mechanical ram at super- and/or subatmospheric pressure. The film serves firstly to protect the contents. It has to protect the contents from the effect of the environment. The film must therefore have a high water-vapor, gas and UV barrier. It must have mechanical stability to protect the contents from physical effects and so that it does not itself become damaged by the contents. The quality of the contents must not be impaired by individual constituents being released from within the film.
Blister packs are increasingly frequently chosen as packaging for a wide variety of articles, since this type of pack is available in a wide variety of forms and meets the requirements of mechanized packaging processes. The starting materials used for blister packs are thermoformable films. These are plastic films which when heated can be shaped relatively readily by applying super- or subatmospheric pressure pneumatically, or using a ram. Appropriate selection of the molds can thus introduce depressions (blisters) into the film (base film) and these can be matched to the shape of the article to be packed. After this shaping step the article to be packed is introduced into the resulting blister. Once the blister has been filled, a backing film is applied to the base film and encloses the article to be packed within its blister.
If all of the requirements cannot be covered by a single material, the properties required in a film are achieved by combining more than one film to give a composite film. Films produced from cycloolefin copolymers have very good impermeability to water vapor. However, these films have poor resistance to fats. Environmental-stress-cracking corrosion occurs on exposure to unsaturated fatty acids.
The film most frequently used in blister packs is polyvinyl chloride (PVC). To increase its barrier properties with respect to gases, in particular water vapor, the amorphous PVC base film is frequently coated with PVDC. Films made from unoriented polypropylene (uPP) give better water-vapor barrier properties than PVC films and are less questionable from an environmental point of view. However, the disadvantage is the poorer thermoformability and higher shrinkage of this partially crystalline material.
The amorphous COC mono- or multilayer films described in EP-A-570 188 and EP-A-631 864, when used as base films, give good processing and good barrier properties.
Relatively new developments in the area of blister packs for pharmaceuticals describe the use of amorphous polyolefins with good processing performance and high water-vapor barriers. For example, EP-A-570 188 and EP-A-631 864 describe the use of polyolefins with cyclic olefins as polymeric building block. These applications describe the use of these polyolefins (cycloolefin copolymers, abbreviated to COC) in the form of mono- or multilayer films for blister packs.
Alongside automated packing and the presentation of the product protected within the blister, for example pharmaceuticals in the form of tablets, capsules or the like, the blister pack can markedly reduce exposure to atmospheric moisture and oxygen and thus increase shelf life.
An object of the present invention is to provide a composite film having a high level of barrier properties and a cost-effective and environmentally friendly process for producing a thermoformable composite film with a high level of barrier properties, very good thermoforming performance and good resistance to fats.
Another object of the present invention is achieved by means of an extrusion-coated film comprising at least one film which comprises cycloolefin copolymer and comprising, on at least one side of this film, a layer of extrusion-coated thermoplastic material.
Extrusion-coating technology comprises the production of films having more than one layer by using extrusion from the melt to apply a thermoplastic to a previously produced film web.
The film web used for the extrusion-coating may be a monofilm, composed of one single layer, or else may itself be a composite film.
The thermoplastics used are mostly readily extrudable products, especially polyethylenes, ionomers or ethylene-vinyl acetate copolymers. Preference is given to the use of polyethylene and particularly LDPE. These materials have good bond strength which prevents subsequent delamination.
Another object of the present invention is achieved by means of a process for producing a thermoformable composite film, where a solvent-free adhesive is used to apply at least one thermoplastic film laminated to a film comprising cycloolefin copolymer.
The object is achieved by means of a process for producing a thermoformable composite film, where a solvent-free single-component adhesive is used to apply the thermoplastic film laminated to the film comprising cycloolefin copolymer.
One novel feature of the process is the use of a solvent-free single-component adhesive for applying a thermoplastic film to a film comprising cycloolefin copolymer in order to produce a thermoformable composite film.
The composite film produced according to the invention is particularly suitable for producing blister packs.
At relative humidity of about 85% and at a temperature of about 23xc2x0 C., the film has water-vapor permeability of xe2x89xa60.05 g/m2d, a puncture resistance of xe2x89xa620 N and a thickness of xe2x89xa6100 xcexcm.